Damage zones

Because of the highly unstable nature of the acid attack in most of the carbonate reservoirs (propagation of wormholes), the development of a descriptive model of the skin evolution was not possible until the recent advent of the theory of fractals. In addition, the characteristics of the damaged zone greatly affect the behavior of the skin during acid injection in any type of reservoir, but particularly in carbonate ones. 

It is assumed that the maximum stress in the next fiber located at a distance dj away is approximately equivalent to the composite tensile strength, cr. It follows then that the damage zone size, cq, for aligned short fiber composites is given by (Lauke et al., 1985)... 

Damage zone size in mode I fracture and corresponding interlaminar fracture toughness values, G j. and Gji,.. of carbon fiber epoxy matrix composites. ... 

System (Fiber/matrix) K,.(%) Mode 1 damage zone size Fracture toughness (kJ/m ) ... 

Chakachery, E.A. and Bradley, W.L. (1987). A comparison of the crack tip damage zone for fracture of HexccI FI85 neat resin and T6T145/FI85 composite. Polym. Eng. Sci. 27, 33-40. 

BlLLl, A., Salvini, F. Storti, F. 2003. The damage zone-fault core transition in carbonates rocks ... 

In the SCG region failure occurs through formation and extension of a fibrillar crack-tip damage zone (following inter-lamellar cavitation and breakdown of inter-lamellar ligaments) as Kc decreases the fibrillar features become progressively finer. 

Figure 13.9 Sequence of events in a croid formation, (a) Initial state at the crack tip. (b) Cavitation ofthe rubber particles dueto loading head of the crack tip. (c) Cavitation of rubber particles near the already cavitated particles due to stress-concentration effect. The croid is forming, (d) Croids are propagating ahead ofthe crack and inside the craze-like damaged zone many shear bands develop between cavitated rubber particles. (Sue, 1992 with kind permission from Kluwer Academic Publisher.)...

Fig. 20 a Side-view of the crack-tip damage zone in a CT specimen of iPP with Mw of 455 kg mol-1 deformed at about 3 m s 1. b Oblique view of the damage zone showing the curved deformation front, c TEM micrograph of the collapsed fibrillar structure of the crack-tip craze, d Detail of structure at the craze-bulk interface [19]... 

Fig. 22a-c BSE-SEM images of crack-tip microdeformation in iPP containing approximately 80 wt% ji phase tested at 0.001 m s 1 and 25 °C. a Overview of the crack-tip damage zone, b and c details from the periphery of the damage zone. The arrows indicate the loading direction [24]... 

Microstructural changes may also influence the nature of the damage zone, given that a more diffuse damage zone would generally be expected to... 

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